The objective of the research is an investigation of cardiovascular responses to systematic changes in pH and a separation of those changes due to hydrogen ion concentration from the changes in blood volume and osmolar concentration. Changes in pulmonary vascular resistance proximal and distal to a Starling resistor in the lung will be measured in the near-term fetal lamb and goat. Changes in blood flow in various systemic areas will be measured in the term fetus as well as the newborn. Changes in the pulmonary and systemic circulation will be measured in the adult dog as well as changes in cardiac output and myocardial contractility. Acidosis will be induced with infusions of lactic and hydrochloric acid, and alkalosis will be produced with infusions of isotonic and hypertonic bicarbonate, THAM, and sodium hydroxide. Some of the work in the fetal animal and also the newborn will be done utilizing radioactive spheres. Some of the fetal work will be done with exteriorized fetuses and other portions with the fetus in utero as a chronic preparation following recovery from surgery and anesthesia in the mother. Blood volume will be measured with I-125- labeled albumin and osmolarity as freezing point depression.